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1Q\ 8905 



Bureau of Mines Information Circular/1982 



Acid Mine Drainage: 

Control and Abatement Research 



By Ann G. Kim, Bernice S. Heisey, 

Robert L. P. Kleinmann, and Maurice Deul 




UNITED STATES DEPARTMENT OF THE INTERIOR 



Information Circular 8905 



Acid Mine Drainage: 

Control and Abatement Research 



By Ann G. Kim, Bernice S. Heisey, 

Robert L. P. Kleinmann, and Maurice Deul 




UNITED STATES DEPARTMENT OF THE INTERIOR 
James G. Watt, Secretary 

BUREAU OF MINES 
Robert C. Norton, Director 







This publication has been cataloged as follows: 



Acid mine drainage. 




(Bureau of Mines information circular ; 8905) 




Bibliography: p. 21-22. 




Supt. of Docs, no.: I 28.27:8905. 




1. Acid mine drainage. I. Kim, Ann G. II. Series: 


Information 


circular (United States. Bureau of Mines) ; 8905. 




-TN2^7U4- [TD899,M5] 622s [628.1'6832] 


82-19724 












CONTENTS 

Abstract 

Introduction 

The acid mine drainage problem 

Chemistry of formation and control 

Bureau of Mines acid mine drainage research 

Mine sealing 

Acid mine drainage treatment 

At-source control of acid mine drainage 

Summary and recommendations 

References 

ILLUSTRATIONS 

1. Ground water percolating through pyrltlc material produces sulfuric acid 

and iron compounds which are eventually discharged into surface streams. 

2. In solutions Inoculated with 0.2 ml of T. ferrooxidans and 0.1 ml each of 

T. ferrooxldans and Metallogenium , the decrease in pH is greater than in 
sterile controls. 

3. Plot of acidity and total dissolved iron versus pH measured in laboratory 

simulations of a coal refuse pile shows the rapid production of acid and 
1 ron at low pH 

4. In abandoned mines below drainage, natural flooding can be used to exclude 

air, limiting pyrite oxidation 

5. A wet seal with an air trap allows water to leave the mine while prevent- 

ing air from entering 

6. Subsidence cracks over an underground mine may allow surface water and air 

to enter a sealed mine 

7 . Although the oxygen level in a sealed mine may be lower than that of nor- 

mal air, it may be sufficient to support oxidation for long periods of 
t Ime 

8. Flow diagram of hydrated lime treatment process for acid mine drainage.... 

9. Although the unit cost decreases with capacity, the total capital costs 

may range between $500,000 and $2 million for a conventional treatment 
process. 

10. Limestone treatment produces a denser sludge in 1 day than lime neutrali- 

zation produces in 43 days 

11. Limestone treatment, which Includes neutralization, aeration, and set- 

tling, is less expensive and produces a dense crystalline sludge 

12. In acid mine drainage neutralized with limestone, the rate of ferrous iron 

oxidation is 10 to 25 ppm/mln 

13. The sequencing batch reactor Incorporates fill, aerate, settle, and dis- 

charge cycles to optimize the rate of ferrous iron oxidation by bacteria 

14. Most sludge from acid mine drainage treatment is retained in ponds, pumped 

into abandoned sections of deep mines, or dumped in refuse areas. 

15. The rate of acid production was approximately that of sterile controls 

when detergent was used to limit bacterial activity in a laboratory 

s tudy 

16. Controlled release of detergents can be used to reduce acid production 

from spoil piles by 50 to 95 pet compared with an untreated control 

TABLES 

1 . Water control practices 

2. Variation in composition of mine effluent before and after sealing 

3. Bureau of Mines conservation and development program — acid mine drainage.. 



Page 



1 


1 


2 


4 


6 


6 


11 


15 


18 


21 



10 

11 



11 

12 
12 
14 
14 
14 

15 
16 



17 
19 

20 



ACID MINE DRAINAGE: CONTROL AND ABATEMENT RESEARCH 

By Ann G. Kim, ' Bernice S. Heisey,^ Robert L, P. Kleinmann,"' and Maurice Deul'' 



ABSTRACT 

Acid drainage from underground coal mines and coal refuse piles Is one 
of the most persistent industrial pollution problems in the United 
States: This Bureau of Mines report reviews the acid mine drainage 
problem generally and describes research currently underway to combat 
it. 

INTRODUCTION 

In the last 15 years there has been little improvement in the number 
of streams adversely affected by acid mine drainage. The Bureau of 
Mines has developed a comprehensive program of acid mine drainage re- 
search oriented toward both active and abandoned mines. It includes im- 
proved prediction of acid potential, improved mine planning, at -source 
control of acid formation, improved reclamation, improved water treat- 
ment techniques, and assessment of ground water contamination in major 
mining districts. 

Controlling the acid at its source by limiting pyrite oxidation is a 
major objective of the program. The Bureau of Mines is investigating 
methods of slowing reaction kinetics by limiting oxygen, inhibiting 
iron-oxidizing bacteria, or otherwise influencing reaction chemistry. 
The Bureau has recently developed and field-tested a practical method of 
bacterial inhibition which is effective in reducing acid drainage from 
coal refuse piles. Since this technique is probably not applicable to 
abandoned underground mines, improved methods of mine sealing are 
required. 

Bureau of Mines research into treatment of acid mine drainage is ori- 
ented toward improving water treatment efficiency and developing low- 
maintenance treatment systems. Current areas of investigation include 
improved iron oxidation efficiency, limestone neutralization, disposal 
of acid mine drainage sludge, and development of an artificial bog 
treatment system. 

'Research chemist. 
^Writer-editor . 
■^Supervisory geologist. 
^Research supervisor. 
All authors are with the Pittsburgh Research Center, Bureau of Mines, Pitts- 
burgh, Pa. 



THE ACID MINE DRAINAGE PROBLEM 



Acid drainage from underground coal 
mines and coal refuse piles is one of the 
most persistent industrial pollution 
problems in the United States. Pyrite in 
the coal and overlying strata, when ex- 
posed to air and water, oxidizes, produc- 
ing ferrous ions and sulfuric acid. The 
ferrous ions are oxidized and produce an 
hydrated iron oxide (yellowboy) and more 
acidity. The acid lowers the pH of the 
water, making it corrosive and unable to 
support many forms of aquatic life. The 
iron oxide forms an unsightly coating on 
the bottom of streams, and further limits 
the ability of aquatic life to survive in 
streams affected by acid mine drainage. 



Before coal is mined, very little of 
the pyrite is exposed to the conditions 
necessary to produce acid drainage. The 
mining and coal cleaning process exposes 
the pyrite to surface or ground waters 
and allows pyrite oxidation to occur. A 
ton of coal containing 1 pet pyritic sul- 
fur has the potential of producing 
33 pounds of yellowboy and over 60 pounds 
of sulfuric acid. However, the rate of 
acid production varies, and abandoned 
mines and refuse piles can produce 
acid drainage for more than 50 years. 
The drainage, if discharged into sur- 
face streams or ponds, constitutes an 
extensive, expensive, and persistent 



-Water percolating 




^^&§^BM 



FIGURE 1. - Ground water percolating through pyritic material produces sulfuric acid and iron com- 
pounds which are eventually discharged into surface streams. 



environmental problem (fig. 1). Federal 
law (37)5 now requires that water dis- 
charge from active coal mines have a pH 
between 6 and 9 and places limits on the 
total iron, manganese, and suspended sol- 
ids. Controlling acid mine drainage from 
active mines usually requires expensive 
water treatment and the necessity of han- 
dling very large volumes of water. Con- 
trolling drainage from abandoned mines is 
even more difficult due to location, 
water volume, and the general limitation 
on public funds available for work in 
this area. The Bureau of Mines research 
program in acid mine drainage addresses 
the problems of both active and abandoned 
mines. 

In 1936, it was estimated ( 17 ) that 
more than 9 million tons of sulfuric acid 
were discharged annually from coal mines 
into the streams of Pennsylvania. Now, 
although Federal and State regulations 
specify water quality standards for coal 
mine discharges, acid mine drainage re- 
mains a problem. The most comprehensive 
survey of the extent of acid mine drain- 
age pollution was conducted by the Feder- 
al Water Pollution Control Administration 
in 1967 (^, 8^). Drainage basins through- 
out the Appalachian Region, in Pennsyl- 
vania, West Virginia, Maryland, Ohio, 
Kentucky, Virginia, Tennessee, Alabama, 
and Georgia, were sampled for various 
water quality parameters including acid- 
ity, to determine the extent of water 
pollution caused by coal mine drainage. 
At that time, 10,500 miles of streams 
were significantly degraded by coal mine 
drainage, and further analysis of the 
data showed that approximately half, or 
5,740 miles was affected by acid mine 
drainage ( 11 ) . 

Since that time, no Federal agency has 
undertaken a survey of this scale; cur- 
rent mine drainage assessments are re- 
stricted to statewide estimates. Direct 
comparisons between current State data 
and those collected in the 1967 study 
cannot be made, because of differences in 

^Numbers in parentheses refer to items 
in the list of references at the end of 
this report. 



the intensity of sampling and variation 
in the criteria used to classify a stream 
as degraded. However, current water 
quality data, obtained from State envir- 
onmental agencies of the Appalachian Re- 
gion, do indicate that there has been 
little overall improvement in streams 
affected by acid mine drainage. 

In Pennsylvania, which annually pro- 
duces approximately 82 million tons of 
coal (22), there are 2,795 miles of major 
streams that fail to meet current water 
quality standards ( 32 ) , Drainage from 
abandoned mines contributes to at least 
70 pet of the total. Although projected 
figures for 1983 indicate a slight de- 
crease in stream miles that will not meet 
water quality standards, no decrease in 
the drainage pollution related to mining 
is expected. 

In Ohio, where annual coal production 
was nearly 42 million tons (22) , a 1979 
study conducted by the Ohio Environmental 
Protection Agency indicates that acid 
mine drainage affects 1,075 miles of 
streams (30). In Maryland, where annual 
coal production was just over 2-1/2 mil- 
lion tons ( 22 ) , the Maryland Bureau of 
Mines currently estimates that 450 miles 
of streams are affected by acid mine 
drainage (9), much of it related to min- 
ing in neighboring States. In Tennessee, 
where annual coal production is nearly 
11-1/2 million tons (22), acid mine 
drainage was estimated to affect 994 
miles of streams, according to the Divi- 
sion of Water Quality Control of the Ten- 
nessee Department of Public Health (35). 
In Kentucky, the Department for Natural 
Resources and Environmental Protection, 
Division of Abandoned Lands, has compiled 
data for 1978-80 which show that of a to- 
tal of more than 2,100 miles of streams 
within the Eastern Coalfield affected by 
coal mine drainage, only 77 miles are 
acid (12). The low proportion of acid 
streams in this area of Kentucky is 
apparently related to the abundance of 
limestone in the coal-bearing rocks. 

Although rigorous comparisons cannot 
be made, the more recent data indicate 
that the extent of acid mine drainage 



pollution is of the same order of magni- 
tude as that measured in the 1967 study. 
Government regulation has done much to 
upgrade the quality of discharges from 
active mining operations, but most acid 
mine drainage comes from abandoned mines, 
which are not regulated. In spite of in- 
creased efforts to control it, acid mine 
drainage continues to be a major problem. 

Present regulations stipulate that acid 
drainage from active mines and refuse 
piles must be chemically treated for as 
long as it is discharged from the mine or 
pile. These mandatory standards have 
generated research needs in the following 
areas: More efficient treatment methods. 



the disposal of sludge produced by treat- 
ment, engineering methods to reduce acid 
formation and other at-source methods of 
control, control of acid formation and 
erosion from spoil piles, and improved 
water management techniques. In addi- 
tion, there is no systematic, cost- 
effective method of reducing the acid 
load from mines already abandoned and 
from mines to be abandoned in the future, 
although an estimated 80 pet of acid mine 
water comes from abandoned mines and 
spoil piles. This area particularly re- 
quires a concentrated research effort if 
there is to be significant improvement in 
the quality of many streams. 



CHEMISTRY OF FORMATION AND CONTROL 



Prevention and/or control of aciiJ mine 
water depends on an understanding of the 
chemical, biological, and geological fac- 
tors that influence its formation, which 
is best described as a series of chemical 
reactions. Acid mine water is produced 
by the oxidation of the pyrite (FeS2) 
normally present in coal and the adjacent 
rock strata. The oxidation of pyrite is 
usually described by the reaction below 
in which pyrite, oxygen, and water form 
sulfuric acid and ferrous sulfate: 

2Fe, + 7O9 + 2HoO = 4H+ + 2Fe2+ + 4S02-. 



Oxidation of the ferrous iron produces 
ferric ions according to the following 
reaction: 

2Fe2+ + 1/2 O2 + 2H+ = 2Fe3+ + H^O. 

When the ferric ion hydrolyzes, it pro- 
duces an insoluble ferric hydroxide (yel- 
lowboy) and more acid: 

Fe3+ + 3H2O = Fe(0H)3 + 3H+. 

Although this summary is correct at pH 
above about 4.0, it is only one of three 
different reactions systems, which vary 
in significance with pH (14). Also 



significant in the oxidation of pyrite is 
a bacterium, Thiobacillus ferrooxidans . 

At near-neutral pH (stage 1), the rates 
of oxidation by air and by T. ferrooxi- 
dans are comparable. This stage is typi- 
cal of freshly exposed coal or refuse. 
Despite the high concentration of pyrite, 
the rate of oxidation either by oxygen or 
by T. ferrooxidans is relatively low, and 
the natural alkalinity of ground water 
may effectively neutralize the acid 
formed at this stage. 

When the neutralizing capacity of the 
environment is exceeded, acid begins 
to accumulate and the pH decreases 
(stage 2). As the pH decreases, the rate 
of iron oxidation by oxygen also de- 
creases. But at the lower pH of stage 2, 
the rate of iron oxidation by T. ferroox- 
idans increases. The action of the bac- 
teria causes increased acid production, 
which serves to further lower pH 
(fig. 2). 

As the pH in the immediate vicinity of 
the pyrite falls to less than 3, the in- 
creased solubility of iron and the de- 
creased rate of Fe(0H)3 precipitation 
affect the overall rate of acid produc- 
tion (stage 3). At this point, ferrous 



lU 



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z 
o 

a: 

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Q. 



6 - 



5 - 



3 - 



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1 


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- 


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1 1 1 1 1 



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INITIAL pH 



8 



FIGURE 2. - In solutions inoculated with 0.2 ml 
of T. ferrooxidans(^) and 0.1 ml each of T. ferro- 



oxi dans and Metallogenium {B), the decrease in pH 
is greater than in sterile controls (C). 



iron is oxidized by T. ferrooxidans and 
the ferric ion in turn oxidizes the 
pyrite: 

FeS2 + 14Fe5+ + 8H2O = 15Fe2+ 

+ S02- + 16H+. 
4 

In this third stage, the rate of acid 
production is high (fig. 3) and is lim- 
ited by the concentration of ferric ions. 
Inhibition of T. ferrooxidans would pre- 
vent ferric oxidation of pyrite and 
should therefore reduce acid production 
by at least 75 pet. 

When untreated acid mine drainage is 
mixed with surface waters, it has a dele- 
terious effect upon the receiving stream, 
usually making it unsightly and inhos- 
pitable to most forms of aquatic life. 
Most organisms cannot tolerate an acid 
environment. Also, the ferrous iron in 
acid mine drainage consumes the oxygen in 
a stream, and the precipitated ferric hy- 
droxide covers the streambed, limiting 
the oxygen available to benthic organ- 
isms. The acidity and total solids ad- 
versely affect aquatic life, and heavy 
metal ions present in some mine waters 
have an increased toxicity in acid 



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1,600 



1,400 



,200 



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800 



600 



400 



200 



I 2 3 4 5 6 7 

pH 

FIGURE 3. - Plot of acidity and total dissolved 
iron versus pH measured in laboratory simulations 
of a coal refuse pile shows the rapid production of 
acid and iron at low pH. 

solutions (6). In streams severely pol- 
luted with acid mine drainage, there are 
usually no complex aquatic plants, no 
fish, few if any benthic invertebrates, 
and only a few species of algae. In some 
cases, the invertebrates and algae that 
can survive grow to nuisance proportions. 

When acid mine drainage is produced in 
an active mine, environmental laws re- 
quire that it meet minimum standards be- 
fore it is discharged into surface 
streams. According to the Federal Water 
Pollution Control Act, water from coal 
mines must have a pH between 6 and 9 and 
must contain no more than an average of 
3.5 ppm and a maximum of 7 ppm iron, no 
more than an average of 2 ppm and a maxi- 
mum of 4 ppm manganese, and no more than 
70 ppm total suspended solids. 

Standard acid mine drainage treatment 
methods Involve neutralization of the 
acid by the addition of a base, oxidation 



of ferrous iron in an aeration tank, or 
pond, and precipitation of iron compounds 
in a settling pond. Manganese, unless 
present in high concentrations, is usu- 
ally removed with the iron. 

The chemistry of the basic treatment 
method is relatively straightforward. 
Neutralization is the reaction of the 
acid with a base: 

H2SO4 + Ca(0H)2 = CaS04 + 2H2O. 

If limestone is used as the neutralizing 
agent, the reaction is 

H2SO4 + CaCOj = CaS04 + H2O + CO2. 

To remove the ferrous iron, the neutral- 
ized water is aerated to produce ferric 
ions, which react with the base to form 
insoluble ferric hydroxides: 

Fe2(S04)3 + Ca(0H)2 = Fe(0H)3 + CaS04. 



With limestone as the neutralizing agent, 
the reaction is 

Fe 2 (504)3 ■•" 3CaC03 + 3H2O = 2Fe(0H)3 
3C0- 



+ 3CaS04 + 



'2* 



Other alkaline agents can be used, but 
because of cost, ease of handling, or 
other environmental effects, lime is most 
commonly used. Other methods that have 
been suggested for treating acid mine 
drainage include reverse osmosis, ion ex- 
change, and flash distillation. However, 
these are not treatment methods per se, 
but methods for producing potable water 
that were suggested for acid mine drain- 
age only where there is no alternative 
source of potable water. With these 
methods a concentrated acid brine or 
sludge must be disposed of, and because 
of technical problems and high cost, 
processes like these are not commonly 
considered as reasonable alternatives to 
neutralization. 



BUREAU OF MINES ACID MINE DRAINAGE RESEARCH 



Methods to reduce the pollution from 
ferruginous acid water from coal mines 
and spoil banks usually involve either 
reducing the rate of acid formation or 
increasing the efficiency of mine water 
treatment. Although acid mine drainage 
has been a problem for many years, there 
have been few significant innovations in 
its prevention and control. The Bureau 
of Mines was involved in much of the acid 
mine drainage research conducted before 
1970 (r7_, ^, 26). The Bureau performed 
analytical studies to determine the acid- 
ity, composition, and corrosivity of acid 
mine water. Sources of and variations in 
acid mine drainage, the effect of pyrite 
content, rock dusting, and chemical neu- 
tralization also were investigated. In 
addition, the Bureau of Mines was a major 
contributor to the development of mine 
seals during the 1930' s. 

During the 1970' s the Bureau of Mines 
had only a limited acid mine drainage 
program as other Federal agencies, such 
as the Environmental Protection Agency 
(EPA), assumed primary responsibility for 
water pollution research. Because of the 



continuing problems in acid mine drainage 
control, the Bureau of Mines has recently 
developed a comprehensive program of 
acid mine drainage research. This pro- 
gram is directed toward several areas, 
including improved prediction of acid 
potential, improved mine planning, at- 
source control of acid formation, im- 
proved reclamation, improved water treat- 
ment, techniques to control acid drainage 
at abandoned mines and waste piles, and 
assessment of ground water contamination 
in major mining districts. 

MINE SEALING 

In 1928 it was reported that mines 
sealed by natural caving produced less 
acid than unsealed mines in the same lo- 
cality (19). It was assumed that limit- 
ing the amount of air and water entering 
the mine reduced the rate of acid forma- 
tion. After a 1-year field study, an ex- 
tensive mine sealing program was under- 
taken in 1933 through the Works Progress 
Administration and the Civil Works Admin- 
istration. Records indicate that seal- 
ing did produce favorable results in 



West Virginia, Ohio, and Pennsylvania 
(36). However, the Federal sealing pro- 
grams were short term and did not provide 
funds for maintaining the seals. Lack of 
maintenance, natural deterioration, van- 
dalism, and subsequent mining combined to 
reduce the long-term effectiveness of the 
mine sealing program. 

Despite the lack of long-term monitor- 
ing, mine sealing is considered a stan- 
dard method for reducing acid formation 
from coal mines (27, 29). In mines lo- 
cated below drainage, natural flooding is 
used to cover the pyritic material and 
exclude air (fig. 4). When the air sup- 
ply is eliminated, it is assumed that the 
pyrite is no longer oxidized. If the 
water pool is stable and the additional 
hydraulic pressure creates no downdip 



Vjj=f. 




drainage problems, flooding is considered 
adequate. 

This effect is currently being observed 
in the Northern Field of the Pennsylvania 
Anthracite Region ( 7^) > where flooded 
workings underlie approximately 43,000 
acres. The Bureau of Mines is currently 
studying the hydrology and geochemistry 
of this large mine pool complex because 
the pool is well established, having 
started to form over 30 years ago. Owing 
to its size and flow characteristics, 
water draining from the mines remained 
acid until only a few years ago, cast- 
ing some doubt on the effectiveness of 
flooding. However, our study has shown 
that the water in the mine pools has now 
recovered and is in fact slightly 
alkaline. 



T<t-, 







FIGURE 4. - In abandoned mines below drainage, natural flooding can be used to exclude 
air, limiting pyrite oxidation. 



In deep mines above drainage, flooding 
is generally ineffective owing to seepage 
through surface fractures and the 
tendency of the water to migrate to other 
discharge points. In such mines, con- 
ventional seals are airtight and/or 
watertight masonry walls hitched into the 
roof, bottom, and ribs of mine openings 
(fig. 5). Subsidence fractures that 
extend from the mine through the caved 
overburden to the surface serve as open 
pathways for the migration of air and the 
drainage of surface water (fig. 6). To 
effectively seal these mines, it is also 
necessary to backfill and grade all 
fractures that extend from the mine to 
the surface. Although aerial photography 
and infrared scanning can be used to 
locate zones of high permeability, this 
process is expensive and not sen- 
sitive enough to delineate relatively 
small subsidence fractures. Indiscern- 
ible joints and subsidence fractures can 
affect the overall effectiveness of a 
mine sealing project by allowing a mine 
to "breathe" (fig. 7). Monitoring by the 
Bureau of Mines has shown a general cor- 
relation between the oxygen level in the 
mine, the differential pressure across 
mine seals, and changes in the barometric 
pressure (28). 

Because most mine sealing evaluations 
are based on short-term observation, the 
Bureau is now evaluating the long-term 
effectiveness of mine sealing in several 
areas. For example, at Moraine State 
Park grouted double bulkhead seals were 
used in an area where an artificial lake 
was built over 10 years ago. In this 
area, water discharged from sealed areas 
has a total mean acid load of 206 lb/day 
10 years after sealing, compared with 540 
lb/day before sealing. The discharge 
rate varies between 250 and 500 gpm, and 
the total iron has a mean value of 
53 lb/day at present, compared with 
46 lb/day prior to sealing (21). Over 
the 10-year period the variation in dis- 
charge rate, acidity, alkalinity, and 
total iron has declined, indicating that 
a mine pool has been created as a result 
of sealing. In the Highland Fuel Mine 
area (Butler County, Pa.) water samples 



are obtained from discharge points and 
from observation holes behind the seals. 
The discharge from the sealed area varies 
from 25 to 80 gpm, and the pH of the 
water is approximately 4. Total iron in 
the discharge averages 12 to 14 ppm. 
Water samples from the mine pool behind 
the seals have an average pH above 6 and 
a higher total iron content. 

Recent inspection of wet, dry, and 
hydraulic and/or bulkhead seals con- 
structed 13 years ago in abandoned mines 
near Elkins, W, Va. , has shown that five 
of the clay seals have deteriorated, al- 
lowing acid seepage to kill vegetation on 
the slopes below the seal. Yellowboy 
precipitate has restricted the drainage 
opening of one wet masonry block seal. 
Water quality in at least one stream 
receiving discharge from the sealed mines 
has not improved significantly since the 
mines were sealed. 

The Bureau's evaluation of mine seals 
installed approximately 10 or more years 
ago has indicated several serious prob- 
lems with conventionally constructed 
seals. First, completely sealing a mine 
above drainage is very difficult and may 
be very expensive. Complete sealing re- 
quires that all zones of high permeabil- 
ity be located and sealed. The usual 
procedure is to locate subsidence frac- 
tures , cover the area with a compacted 
clay blanket, and regrade it. To be ef- 
fective, this procedure requires that all 
fractures be located and that no further 
subsidence occur. The evidence indicates 
that surface sealing is rarely effective 
for long periods. Another problem with 
mine sealing is that masonry seals re- 
quire continued maintenance. Even if 
seals are adequately built and main- 
tained, the improvement in water quality 
directly attributable to the sealing pro- 
cess has not been adequately determined. 

To improve the effectiveness of mine 
sealing, the Bureau of Mines is studying 
sealed mines to determine factors con- 
trolling changes in water quality and is 
developing techniques to build more 
efficient, less expensive seals. In 



Hitch- 



/y///A/ ,, /i, ^ //•/,,/ . 



,_ Hitchx ^ 

J — . C-4 




ELEVATION-A 



Roof rock 




FIGURE 5. - A wet seal with an air trap allows water to leave the mine while 
preventing air from entering. 




FIGURE 6. - Subsidence cracks over an underground mine may allow surface 
water and air to enter a sealed mine. 



10 



22 



O 14 




KEY 

— Sealed mine I 

— Sealed mine 2 




15 20 

TIME, months 

FIGURE 7. - Although the oxygen level in a 
sealed mine may be lower than that of normal air, 
it may be sufficient to support oxidation for long 
periods of time. 

addition to monitoring discharge rates 
and water quality parameters, at some 
sites drawdovm testing will be used to 
determine aquifer capacity and water 
level fluctuations. Subsidence areas 
will be surveyed during and after draw- 
down testing. The collection of rainfall 
data and the use of fluorescent dye to 
determine the direction and velocity of 
ground water flow in the mine pool will 
also be used to determine the factors 
that affect water quality when mines are 
sealed conventionally. 

The Bureau also is involved in a demon- 
stration of pneumatic stowing of lime- 
stone as a method of producing more 
effective mine seals at a cost equal to 
or less than that of conventional seals. 
Observations of mine seals to date indi- 
cate that seals constructed of cement 
block and grout do not substantially im- 
prove water quality, may not effectively 
contain impounded water, and are subject 
to failure and/or leakage. The construc- 
tion of a competent seal requires that it 
be permanently attached to the roof, 



ribs, and floor. Frequently the failure 
of conventional seals is due to collapse 
of weak strata over the seal. Pneumatic 
stowing produces a highly compacted lime- 
stone plug which supports roof and ribs. 
Movement of surrounding strata will cause 
further compaction of the limestone. 
Concrete or other additives to the lime- 
stone can be used to produce a stronger 
seal. If appropriate, the limestone seal 
can be constructed to allow low flows 
of mine water. If the water is only 
slightly acid, passage through the lime- 
stone can effectively neutralize it. In 
a field trial of pneumatic stowing, the 
limestone seals were found to be satis- 
factory in terms of the safety of con- 
struction, the strength of the seal, and 
the cost. Long-term monitoring of these 
seals is planned to determine their 
effect on water quality. 

In deep mines, the construction of mine 
seals limits the water discharge rate and 
creates a mine pool covering some or all 
of the pyritic material. If inundation 
is to be an effective method of con- 
trolling acid drainage, outcrop barrier 
pillars must be capable of withstanding 
the hydrostatic head created by the im- 
pounded water. In general. Federal and 
State regulations on mine closure do not 
deal directly with criteria for outcrop 
barriers used to flood the mine. A 
Bureau of Mines contract report (31) de- 
tails the factors that affect the com- 
petency and stability of outcrop barri- 
ers. According to the study, an outcrop 
barrier should be wide enough to prevent 
seepage, have sufficient overburden to 
prevent a blowout, and provide a stable 
slope. Curtain grouting, compartmental- 
ized barriers, and relief wells can be 
used to reinforce outcrop barriers. 

In mines that have been successfully 
inundated, water quality is often good in 
the mine pool but generally acid after 
seeping through the barrier. Use of a 
relief well system, as suggested in the 
contract report (31) , would remove water 
from the mine pool prior to its exposure 
to pyrite-bearing coal and would also 
limit the hydrostatic head that the out- 
crop barrier would have to withstand. 
Properly designed outcrop barriers could 



11 



reduce acid formation in abandoned mines 
and allow maximum coal removal. 

Oxygen may also be a limiting factor in 
coal refuse piles and some surface mines. 
The Bureau of Mines is currently using 
soil gas probes to study oxygen diffusion 
characteristics in coal refuse piles; 
preliminary results indicate that pyrite 
oxidation is limited to a near-surface 
layer. A similar study will soon be ini- 
tiated in an abandoned surface mine. 
Followup research will concentrate on 
current reclamation methods to determine 
if any reduce oxygen diffusion or result 
in the consumption of oxygen, thus limit- 
ing acid formation. 

ACID MINE DRAINAGE TREATMENT 

Many factors influence the quantity and 
quality of water handled by a mining 
operation, but it is not unusual for a 
single mine to treat Ijnillion gallons of 
acid water per day. Water from coal 
mines is usually treated by chemical neu- 
tralization. At present, lime is the 
most commonly used neutralizing agent. 
Generally, a small volume of mine water 
is added to powdered lime to produce a 
slurry which, added to the raw mine 
water, raises the pH to between 7 and 9. 
The water is aerated to oxidize the fer- 
rous iron and is then transferred to a 
settling pond for precipitation of the 
iron compounds (fig. 8). Although com- 
monly used, lime neutralization has sev- 
eral inherent problems. Lime is a 
caustic material and can produce water 
with an unacceptably high pH. Lime 
treatment produces a flocculant precipi- 
tate that does not form a dense, easily 
handled sludge. Research by EPA failed 
to produce any economical improvement in 
sludge disposal methods. The Bureau is 
evaluating the technology and economics 
of current sludge disposal practices to 
determine the most promising area of re- 
search. Sludge disposal problems, and 
high cost (fig. 9) are the principal rea- 
sons for seeking improved acid mine 
drainage treatment methods. 



Row cool 
mine water 




Lime 

storage 

bin 



Flash 
mixer 



Lime 
screw 
feeder 



Oxidation 
tank 



Sludge 

collection 

pump 





Settling 

lagoon 

I 



1 ' 






Settling 

lagoon 

2 




Settling 
lagoon 

3 










1 e 



Plant 
effluent 



FIGURES. - Flowdiagramofhydrated lime treat- 
ment process for acid mine drainage (34). 



CAPACITY, gal/d 



1,000 



500 



;I00 



50 




J I I I I 



J I I I I I II 



J I I I I I I 



10^ 



CAPACITY, mVd 



10^ 



FIGURE 9. - Although the unit cost decreases 
with capacity, the total capital costs may range 
between $500,000 and $2 million for a convention- 
al treatment process (34), 



12 



As an alternative treatment method, the 
Bureau has developed a neutralization 
process using limestone instead of lime 
(4^, 61, ]A, l]_, 24-25). Limestone is 
readily available and costs less than 
lime, and limestone treatment produces a 
dense crystalline sludge (fig. 10). In 
the Bureau treatment process, very fine 
(5 to 10 ym) limestone is produced by wet 
autogenous grinding in a tube mill. The 
limestone slurry is mixed with the acid 
mine drainage, and the drainage is aer- 
ated to remove carbon dioxide and to oxi- 
dize the ferrous iron (fig. 11). The 
gypsum-iron oxide sludge separates from 
the drainage in settling ponds. Although 
limestone treatment has the advantages of 
lower material costs, simplicity of plant 
design and operation, the use of a less 
hazardous material, and a denser, sludge, 
its use is limited by the rate at which 
ferrous iron is oxidized. With limestone 
neutralization, the pH of the treated 



12 



0) 

a 
S 10 



E 

o 
o 

E 

LiT 



UJ 

o 

Q 

_l 
CO 



8 










KEY 
P^ Lime 

[//^ Limestone 



IS 



:V,Ti>1^(: 







"SUM 






^S 




5 43 
SETTLING TIME, days 

FIGURE 10. - Limestone treatment produces a 
denser sludge in 1 day than lime neutralization 
produces in 43 days. 



drainage is between 6.8 and 8.0 and the 
iron oxidation rate ranges from 10 to 
25 ppm/min (fig. 12). 

To minimize the power and land require- 
ments for aeration, the Bureau is inves- 
tigating the use of catalysts to increase 
the rate of ferrous iron oxidation at low 
pH. A laboratory study by the Bureau of 
Mines indicated that activated carbon was 
an effective catalyst in the oxidation of 
ferrous iron (23). In batch tests, the 
ferrous iron content of acid mine drain- 
age flowing through an aspirated column 
of activated carbon was reduced from over 
700 ppm to less than 10 ppm in approxi- 
mately 1 minute. In these tests, approx- 
imately 5,000 ml of the acid drainage was 
passed through the 200 grams of activated 
carbon before the catalytic effect was 
noted. During this period the pH of the 
effluent was higher than that of the mine 
drainage feed. Since the increase in 
iron oxidation rate was observed after 
the pH of the drainage showed substan- 
tially no change, the onset of the cata- 
lytic effect was attributed to acid con- 
ditioning the carbon, 

A pilot-scale field study was conducted 
(33) to study the effect of activated 
carbon on the ferrous iron oxidation rate 
using a three-stage continuously stirred 
reactor. Continuous agitation of the 
carbon in the mine water provided more 
efficient water-carbon contact and pre- 
vented channeling and/or fouling. A weir 
device at the top of the reactor con- 
trolled carbon loss. In this system the 
ferrous iron oxidation rates were not as 
high as those reported in the previous 
laboratory study. Acid conditioning the 
carbon did not significantly affect the 
iron oxidation rate. When the pH of the 
influent water was adjusted to 5, the 
rate of iron oxidation increased, but not 
to the levels reported in the laboratory 
study. When comparing the rate data from 
the field and laboratory studies, it was 
considered possible that the high iron 
oxidation rate reported was due to the 
growth of iron-oxidizing bacteria on the 
carbon rather than to direct catalysis by 
the carbon. T. ferrooxidans is an aero- 
bic bacterium which derives energy from 



13 



Mine discharge 
from borehole 



Makeup limestone 
Autogenous tube mill, 25 rpm, ^^^^ 3 in by 
7,500- to 9,000-1 b limestone load, ' 

about 80 pet C0CO3 



Limestone slurry sump, ['] 
6to8.7lb/min U / 

<400"mesh size 




Mine water analysis : 
PH, 2.8 
Fe**, 36 ppm 
Total Fe, 360 ppm 
Acidity, 1,690 ppm 



Effluent 
pH, 5.7 



Aeration pond 



Weir 
Effluent pH, 6.8 
Fe, 3 ppm 



Sedimentation pond 



Discharge to main lagoon 
pH, 7.0 

Fe, < I ppm 



FIGURE 11, - Limestone treatment, which includes neutralization, aeration, and settling, is 
less expensive and produces a dense crystalline sludge. 



the oxidation of ferrous iron in acid 
mine drainage. It is possible that the 
activated carbon provides a substrate to 
which the bacteria adhered. However, 
recent laboratory tests showed no signif- 
icant bacterial activity or catalytic 
action. 

The Bureau is also funding an investi- 
gation of the growth of iron-oxidizing 
bacteria on clay particles (5,000 mg/l) 
in a sequencing batch reactor. In this 
test bacteria are grown on clay particles 
in a ferrous sulfate solution containing 
appropriate inorganic nutrients. The re- 
actor, a system of fill, aerate, settle, 
and discharge cycles (fig. 13), is de- 
signed to produce an effluent with a Fe2+ 
concentration of less than 10 mg/l. The 
retention of bacteria on the clay par- 
ticles is dependent upon the ferrous iron 
content. If the Fe2+ content of the 



system decreases to 5 mg/l, the bacteria 
are desorbed from the clay and removed 
from the reactor in the discharge cycle. 
Using the sequencing batch reactor, a 
ferrous iron oxidation rate of approxi- 
mately 290 mg/l/hr has been reported for 
estimated bacterial populations of ap- 
proximately 5 X 10^ cells/ml. 

The disposal of sludge produced by neu- 
tralization of acid mine drainage is ex- 
pensive and potentially one of the most 
persistent problems in its treatment. As 
a preliminary step, the current sludge 
disposal practices of 33 treatment plants 
were assessed to determine the magnitude 
of sludge production, current disposal 
practices, and constraints on their usage 
(1). The primary sludge disposal problem 
involves the large volume of sludge gen- 
erated and the scarcity of approved dis- 
posal sites. The four most commonly used 



lA 



800 



700 - 



600 - 



500 - 



I 

Q. 

^ 400 



300 - 



200 - 



100 



1 -r 


1 I 1 


1 


- \\ 




- 


\ \ 


\ 


~ 


- \ \ 


\ N 
\ S 
\ N 


- 


^^ 


\ 1 1 >^ ^^ 


4-^ 



10 15 20 

MIXING TIME, mm 



25 



■30 



35 



FIGURE 12. - In acid mine drainage neutralized 
with limestone, the rate of ferrous iron oxidation is 
10 to 25 ppm/min» 



V////.m^///////////////////777Zy 



Settle 



2 4 6 8 10 

BATCH REACTOR SEQUENCING CYCLE TIME, hr 



12 



FIGURE 13. - The sequencing batch reactor in- 
corporates fill, aerate, settle, and discharge cycles 
to optimize the rate of ferrous iron oxidation by 
bacteria. 

methods of sludge disposal are deep mine 
disposal, retentzion in ponds, incorpora- 
t:ion in coal refuse piles, and surface 
burial. The amount of land required for 
disposal is usually the determining fac- 
tor in the overall cost, although trans- 
portation, equipment, maintenance, and 
labor are also significant (fig. 14). 
The development of methods to efficiently 
and economically increase the density of 
the sludge would substantially reduce the 
cost of sludge disposal. 

Although there are other methods poten- 
tially applicable to acid mine drainage 



Deep mine 



Retained in pond 



Refuse area 



Burial on site 




33 AMD plants surveyed 
Total area: 214 acres 



KEY 
^3 Pet AMD plants 
Pet total acreage 
Average area, acres 

I I Maximum area per 

site, acres 
J L 



100 



20 40 60 80 

FIGURE 14. - Most sludge from acid mine drain- 
age (AMD) treatment is retained in ponds, pumped 
into abandoned sections of deep mines, or dumped 
in refuse areas. 

treatment, such as ion exchange, reverse 
osmosis, and flash distillation, the Bu- 
reau is not currently investigating 
these. Most of these processes are high 
in cost, have high power requirements, 
and produce a highly concentrated toxic 
brine or sludge which is more difficult 
to dispose of than the original sludge. 
The Bureau's research program in treating 
acid drainage from active mines is di- 
rected toward development and demonstra- 
tion of a complete limestone treatment 
system, including a suitable catalyst for 
rapid oxidation of ferrous iron and 
sludge disposal. 

The Bureau is also investigating a low- 
cost, low-maintenance treatment system 
for small streams contaminated by acid 
drainage from abandoned mines. Conven- 
tional treatment is not applicable be- 
cause of the low flow rate and the remote 
rural location. It has been observed 
that bogs containing sphagnum moss and/or 
cattails remove iron by ion exchange and 
precipitation (10). Subsequent neutrali- 
zation at limestone outcrops completes an 
effective natural treatment system. 
Artificial duplication of this natural 
process could improve water quality in 
many small streams. 

The Bureau will test the practicality 
of duplicating this natural treatment 
system at a low-flow acid drainage dis- 
charge point in Northern Appalachia. 



15 



The system will include an artificial 
sphagnum moss bog followed by limestone 
rubble. The system is designed so that 
the drainage will pool in the moss, but 
will not raise the upstream water level 
enough to allow the water to flow around 
the treatment system. Monitoring the pH, 
Eh, temperature, iron and sulfate concen- 
trations, and total acidity of the stream 
above and below the artificial bog will 
determine its effect on water quality. 
The monitoring will extend over at least 
6 months so that the effect of uncon- 
trollable parameters such as ambient tem- 
perature, rainfall, and stream flow rate 
can be determined. If this low-cost, 
low-maintenance system proves to be ef- 
fective, it could be used to restore many 
small streams in rural areas. 

AT- SOURCE CONTROL OF ACID MINE DRAINAGE 

Of the millions of dollars spent on 
acid mine drainage each year, the major 
portion is spent on treatment. But 
treatment is not the best solution to 
most acid mine drainage problems. Treat- 
ment has the disadvantage of being nec- 
essary for as long as the acid discharge 
continues and thus requires manpower, 
surface facilities, and a sludge disposal 
area indefinitely. 



West Virginia (16). Sodium lauryl sul- 
fate was applied at rates of 20 to 55 gal 
of 30-pct solution per acre, with a dilu- 
tion range between 1:100 and 1:1000. 
Application rates were based on labora- 
tory adsorption tests; dilution rates 
were dictated by site characteristics. 
At each site, drainage pH rose from ap- 
proximately 2.5 to 5.5 or higher, with 
similarly dramatic decreases in acidity, 
iron, and sulfates. 

One disadvantage of the detergents is 
that their effectiveness is limited; re- 
population of the bacteria typically 
occurs in 3 to 4 months. To provide 
long-term control, the surfactants have 
been incorporated into rubber pellets 
(16) which can be applied early to a 
refuse pile or pyrite mine spoil. These 
pellets gradually release the surfactant 
into infiltrating rain water. In labora- 
tory studies (fig. 15) and pilot-scale 
tests (fig. 16), controlled release of 
sodium lauryl sulfate reduced acid pro- 
duction 50 to 95 pet (14). Full-scale 
field tests are now in progress. 

Another potential approach to at-source 
control of acid production requires the 
establishment of an alkaline environment. 
As already discussed, pyrite oxidation is 



Since acid drainage results from the 
oxidation of pyrite associated with coal 
and overburden strata, limiting the rate 
of pyrite oxidation would reduce the 
amount of acid formed. T. ferrooxidans 
normally catalyzes the pyrite oxidation 
and accelerates the initial acidification 
of freshly exposed coal and overburden. 
Inhibiting bacterial activity, therefore, 
would limit the rate of acid production 
and, in combination with proper reclama- 
tion, would reduce substantially the to- 
tal amount of acid produced. Of the mul- 
titude of potential bactericidal agents, 
certain biodegradable anionic surfactants 
(detergents) have been found to control 
T. ferrooxidans in an economical and 
environmentally safe manner (15). 

Field tests were recently conducted 
by the Bureau of Mines on both active 
and abandoned coal refuse piles in 



5,0001^ 




1,000 



3,000 



2,500 



E 

Q. 
CL 



- 2,000 ^ 

_j 



1,500 



1.00 



1,000 



0.25 0.50 0.75 
AMOUNT OF CONTROLLED 
RELEASE MATERIAL, g 

FIGURE 15. - The rate of acid production was 
approximately that of sterile controls when deter- 
gent was used to limit bacterial activity in a lab- 
oratory study. 



16 



35.000 



g"^ 30,000 

o 
o 



E 

ro" 
00 

X 

Q. 



Q 

O 
< 



5,000 - 




70 100 130 

AGE OF COAL REFUSE PILES, days 

FIGURE 16. - Controlled release of detergents can 
beused to reduce acid production from spoil piles by 
50 to 95 pet compared with an untreated control. 

slow at near-neutral pH. A source of 
alkalinity such as lime, if added to 
recently exposed pyritic material, will 
retard or prevent acidification. The Bu- 
reau of Mines is currently investigating 
the possibility of reestablishing a radi- 
cally alkaline environment, albeit tem- 
porarily, to determine if this will slow 
pyrite oxidation to the point where lime- 
stone will be sufficient to maintain 
near-neutral pH. 

Water handling procedures for under- 
ground coal mines generally combine grav- 
ity flow and collection with pumping from 
sumps to surface treatment and/or dis- 
posal areas. To minimize the formation 
of acid water, properly placed sumps and 
pumping systems can reduce the time the 
water is in contact with pyritic materi- 
als. The size and location of sumps is 
also governed by the ability to discharge 
water on the surface with minimum power. 



depends upon 
t ration of 
a treatment 
control 
reduce 



Since on the average it requires 0.5 kwhr 
to pump 1,000 gal of water against a 100- 
ft head, gravity drainage and an effi- 
cient pump are most cost effective. The 
capacity of water treatment facilities 
flow rate and the concen- 
pollutants. In designing 
system, using infiltration 
and efficient water handling to 
the amount of water flowing 
through the mine and minimize the amount 
of acid formed can result in substantial 
savings in water treatment costs. 

A recent Bureau of Mines contract study 
examined current state-of-the-art methods 
of water diversion and overburden de- 
watering in Appalachian bituminous coal- 
fields (3). It was found that most water 
enters underground mines either through 
water-bearing strata in contact with the 
coal seam, from surface seepage, through 
faults and fractures, or from abandoned 
workings. If surface water is the 
source, runoff diversion, regrading, soil 
sealing, and streambed modifications are 
possible control methods. The influx of 
ground water may be controlled by reduc- 
ing the permeability of overlying strata, 
sealing abandoned mines , and well de- 
watering in advance of mining. Although 
all of these methods have been tried to 
some extent (table 1), their successful 
application depends largely upon geologic 
and hydrologic conditions. In general, 
the standard approach to handling the in- 
flux of water into underground mines con- 
sists of collecting the water and pumping 
it back to the surface. At present it 
appears that water diversion and over- 
burden dewatering are, at best, sup- 
plements to traditional water handling 
procedures. Such methods have the 
advantages of helping to control large 
influxes of water that could affect pro- 
duction and reducing the cost of water 
treatment. 



TABLE 1. - Water control practices (2) 



17 



Water control 
practice 



Application 



Limits of control 



Field experience 







SURFACE WATER CONTROLS 




Runoff 


diversion. . . 


Prevents infiltration into 


Effective if mine inflow 


Used with varying 






soil, mine openings, out- 


is due to infiltration. 


success. 






crops, rock fissures, strip- 


May increase stream flow. 








pings, cave-ins, surface 










cracks, and subsidence areas. 






Surface 


! regrading,. 


Eliminates ponding and im- 


Depends on drainage area. 


Used at strip mine 






proves drainage. Applicable 


annual precipitation. 


sites. Can be very 






near surface mines or other 


rate of infiltration in- 


effective if mine 






large land disturbances. 


to soil. May increase 
stream flow. 


water is due to 
ponding of water 
over mine. 


Soil sealing 


Prevents infiltration 


Prevents infiltration into 


Limited success. 






into soil by reducing 


soil only. Not effective 








permeability. 


in sealing fractures or 
other flow conduits. 




Stream 


channeling. . 


Prevents inflow to mines from 
streams, especially in areas 
of vertical fractures, 
subsidence, or high 
permeability. 


Can prevent large quan- 
tities of water from 
entering a mine. 


Very effective. 





GROUND WATER 


CONTROLS 




Grouting and/or 


Reduces permeability of over- 


Effective in limiting in- 


Effective in curtail- 


grouting curtains. 


lying strata by sealing fis- 


flow via direct conduits. 


ing water inflow 




sures, fractures, and perme- 




during shaft sink- 




able formations. 




ing. Also used to 
cement localized 
areas of water in- 
flow such as faults 
and joints. 


Borehole sealing... 


Prevents inflow to mines 


Sealing ineffective after 


Effective in reducing 




through boreholes from sur- 


roof collapses. 


inflow through 




face water sources and/or 




boreholes. 




overlying aquifers. 






Subsurface soil 


Prevents infiltration through 


Sealing efficiency re- 


No demonstrations of 


sealing. 


the soil by reducing 


duced if area frac- 


this technique. 




permeability. 


tured. Most sealants 
are uneconomical. 




Mine sealing 


Prevents water from escaping 


Seals may lose effective- 


Effective in reducing 




an abandoned mine and infil- 


ness with time, depending 


or eliminating flow 




trating active workings. 


on construction method 


from abandoned mines 






and strata changes. 


into active mines. 






Seals may cause ground 








water levels to rise, 








causing surface damage. 








Breached seals may prove 








hazardous to adjacent op- 








erating mines. 




Well dewatering .... 


Intercepts aquifers and 


Requires favorable geo- 


Limited success. 




controls the movement 


logic conditions. 


Used in reducing 




and discharge of 




water handling re- 




groundwater. 




quirements in mine. 



18 



In coal mines where fracture-dominated 
inflow is localized, intercepting water 
entering through faults and fractures may 
be feasible. Water flowing through such 
fracture zones is essentially surface 
water and would not normally require 
treatment. The Bureau has awarded a 
contract to conduct a pilot study on 
controlling fracture-dominated inflow. 
The study will develop design criteria 
for, and determine the cost effectiveness 
of, intercepting nonacid water flowing 
through localized fractures and trans- 
porting it to the surface. Economic and 
engineering analysis of this process 
should determine if it would reduce the 
cost of treatment substantially. 

Coal storage piles and refuse piles may 
also be sources of ground water contam- 
ination (38). Rainfall percolating 
through such piles may leach acid and/or 
other toxic ions and carry them into 



ground water. The Bureau has awarded a 
contract to assess the extent of ground 
and surface water contamination from coal 
storage piles. Methods to prevent con- 
tamination of ground water include sur- 
face collection, impoundment, and treat- 
ment of runoff water. Preliminary cost 
estimates and a discussion of beneficial 
and adverse effects will be included. 

Another area of concern is the effect 
of large-scale lignite mining in western 
Tennessee on ground water resources. At 
present there are few data available on 
the effects of mining upon ground water 
in the alluvial plain, in both shallow 
and deep aquifers. To gather data, four 
wells and two pits have been dug to de- 
termine ground water levels, movement, 
and chemistry. A contract report will 
assess the hydrologic impact of lignite 
mining. 



SUMMARY AND RECOMMENDATIONS 



The Federal Water Pollution Control Act 
of 1972 set effluent standards for coal 
mines, requiring treatment for acid mine 
drainage. Although these standards have 
been in effect for almost a decade, there 
has not been significant improvement in 
the water quality of many streams af- 
fected by mine drainage. This lack of 
improvement is related to the amount of 
acid drainage flowing from abandoned 
mines. 

It has been known for years that air, 
water, bacteria, and pyrite are essential 
elements in acid production, yet at pres- 
ent there is no standard method or pro- 
gram for limiting the formation of acid 
mine drainage. Controlled release of 
anionic surfactants appears to be 
applicable to near-surface sources of 
acid production but not to long-term 
treatment of underground mines. Mine 
sealing, which is supposed to limit acid 
production in abandoned mines, has been 
only marginally successful (table 2). 
Bureau of Mines studies indicate that 
surface reclamation and seals at mine 
openings do not retard the passage of air 
into a mine. In many cases, seals used 



to flood a mine or the surrounding strata 
cannot withstand the continuous hydraulic 
pressure, resulting in failure of the 
seal or seepage around it. The Bureau is 
now evaluating mine seals in several are- 
as in order to determine relevant chemi- 
cal, geological, and engineering param- 
eters and to determine the long-term 
effect of mine sealing on water quality. 

Mine sealing is relevant not only to 
abandoned mines, but also to operating 
mines that will close in the future. At 
the present, mines must eliminate acid 
production or treat acid drainage in- 
definitely. It is possible that bond 
forfeiture may become a realistic eco- 
nomic alternative to the long-term cost 
of water treatment. In this area, there 
is need for development of low-cost seals 
that will maintain their integrity in- 
definitely. Other methods such as con- 
trolled roof collapse, water diversion, 
bacterial inhibition, and improved drain- 
age should be investigated to determine 
their usefulness in reducing the forma- 
tion of acid in mines that are no longer 
operating. 



19 



TABLE 2. - Variation in composition of mine effluent before and after sealing 



Mine 1 



Before 



Low 



High 



After 



Low 



High 



Mine 2 



Before 



Low 



High 



After 



Low 



High 



2.9 
75 
655 
203 
109 
13 



3.2 

1,290 

2,260 

1,242 

520 

508 



PH 

Total acidity (as CaCOj)! , .ppm. . 

Sulfate (as SO4 ) ppm. . 

Calcium (as CaCO^) ppm.. 

Magnesium (as MgCOj ) ppm. . 

Total iron (as Fe203) ppm.. 

lEnd point = pH 8.2 at 60° C. 



Improved prediction of acid drainage 
potential is being investigated in order 
to eliminate or minimize the formation of 
acid mine drainage. At present, core 
samples are analyzed for total sulfur and 
potential alkalinity, or tested with slow 
leaching methods. These procedures have 
not been correlated with acidity mea- 
surements in the field, and they are gen- 
erally acknowledged as only an approx- 
imation of potential acid problems. 
Available techniques will be tested at 
sites where the extent of acid production 
is known, to determine their accuracy and 
possibly develop modifications. Rapid- 
leaching tests will also be examined for 
their applicability to the determination 
of acid potential. Accurate methods of 
predicting acid potential of coal and 
overburden will allow better permitting 
by State agencies, improved mine plan- 
ning, and improved reclamation. 

In operating mines, the need to treat 
large volumes of acid drainage is a 
problem. Currently, lime neutralization 
with aeration is the standard method of 
treating acid mine drainage. This method 
is relatively expensive, requires hand- 
ling a caustic substance, and produces a 
sludge with poor settling characteris- 
tics. The Bureau has developed and is 
now improving a treatment system using 
limestone. Limestone treatment is less 
expensive, uses a noncaustic material, 
and produces a denser sludge. Routine 
use of the system requires the rapid oxi- 
dation of ferrous iron at acid or neutral 
pH. In an initial field study, activated 



3.0 
45 

356 

36 

76 

5 



5.5 
490 
1,180 
625 
336 
160 



2.3 

80 

349 

125 

76 

33 



3.2 
1,210 
2,520 
760 
530 
670 



2.85 

20 

152 

70 

7 

23 



3.70 

1,170 

2,375 

725 

502 

720 



carbon did not have the anticipated 
catalytic effect on the iron oxidation 
rate. Presently, studies are underway to 
determine if iron-oxidizing bacteria 
grown on activated carbon can increase 
the rate of iron oxidation in acid mine 
drainage. A study using bacteria grown 
on clay particles in a sequencing batch 
reactor has the same purpose. The 
develop-ment of an effective oxidation 
step will allow full-scale testing of the 
limestone treatment process. At present, 
other methods of treating acid mine 
drainage are not economically or tech- 
nically practical. Limestone treatment 
seems to be one alternative that could be 
technically feasible and economically 
superior to lime treatment, although at 
present it is primarily applicable to 
waters with a low ferrous iron content. 
It also has the advantage of being read- 
ily adaptable to reclaiming streams 
affected by drainage from abandoned 
mines. A passive system using sphagnum 
moss and limestone will be tested as a 
means of improving water quality in low- 
flow streams. 

It is apparent that 10 years of man- 
dated water treatment have not produced a 
significant improvement in overall water 
quality. Although treatment of acid 
drainage from active mines prevents fur- 
ther deterioration, the majority of mine 
water pollution originates from abandoned 
mines. At present there is a need to 
develop methods for reclaiming polluted 
streams and for at-source control of 
acid production. Research is needed to 



20 



develop limestone treatment into a prac- 
tical alternative to lime neutralization. 
To address these and other acid mine 
drainage pollution problems, the Bureau 
of Mines is conducting research in bac- 
terial inhibition to control acid genera- 
tion, improved water handling to reduce 
acid load, development of improved mine 
seals, rapid biological oxidation of fer- 
rous iron, improved sludge disposal prac- 
tices, low-maintenance treatment of small 
streams, reclamation techniques to reduce 



acid drainage formation, and limestone 
treatment of acid drainage (table 3). 

Work in these research areas comprises 
a comprehensive approach to solving many 
of the longstanding problems associated 
with acid mine drainage. Improved treat- 
ment methods, at-source control methods, 
and stream reclamation methods resulting 
from the Bureau's research program will 
make a significant contribution to up- 
grading water quality in mining areas. 



TABLE 3. - Bureau of Mines conservation and development program — acid mine drainage 



Research area 

Prediction of acid mine drainage: 

Prediction of acid potential 

Prediction of water infiltration 

Integration of predictive technology and premine planning 

At-source control technology: 

Inhibition of acid-forming bacteria: 

Surface mines and refuse piles 

Tailings piles 

Extension of bacterial inhibition to underground mines where 

applicable 

Alkaline treatment of coal refuse 

Placement of phritlc overburden 

Water handling procedures, including diversion and dewatering 

At-source control technology for inactive or abandoned mines: 

Daylighting 

Effect of flooding on acid production, limiting parameters 

Improved mine seals 

Feasibility study — underground disposal mine refuse in a flooded mine 

Demonstration of above if feasible 

Reclamation of acid seeps (burnout) on revegetated mine sites 

Water treatment: 

Enhanced oxidation of iron 

Limestone neutralization 

Improved sludge disposal 

Assessment studies: 

Ground water contamination by acid-producing metal ore mines and 
t ai lings ponds 

Economic analysis — recovery of metals from tailings or streams 

Manuals : 

Premine planning to minimize acid drainage 

At-source control of acid drainage 



Proposed 
time frame, 
fiscal years 



1981-85 
1981-84 
1984-86 



1981-83 
1983-84 

1983-86 
1982-83 
1982-85 
1981-85 



1982-85 
1982-85 
1981-86 
1982-83 
1984-85 
1982-85 



1981-86 
1984-86 
1982-84 



1982-86 
1983-85 



1985-86 
1985-86 



21 



REFERENCES 



1. Ackman, T. E. Sludge Disposal 
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2. Appalachian Regional Commission. 
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22 



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35. Tennessee Department of Public 
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105 pp. 



INT.-BU.OF MINES, PGH., PA. 26485 



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